Resin composition eliminating volatile loss of initiating species for the preparation of printed circuit board laminates

ABSTRACT

An enhanced prepreg for printed circuit board (PCB) laminates includes a substrate and a resin applied to the substrate. The resin includes a curable polymer and a polymerization initiator polymer having a backbone with a free radical initiator forming segment that breaks apart upon being subjected to heat to generate a plurality of non-volatile initiating species. This resin composition eliminates possible volatile loss of the free radical initiator during all processing steps in the preparation of PCB laminates. The resin may additionally include a cross-linking agent, flame retardant and viscosity modifiers. In one embodiment, a sheet of woven glass fibers is impregnated with the resin and subsequently dried or cured. The glass cloth substrate may include a silane coupling agent to couple the resin to the substrate. In another embodiment, resin coated copper (RCC) is prepared by applying the resin to copper and subsequently curing the resin.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a divisional application of pending U.S.patent application Ser. No. 12/860,117 (docket no. ROC920100061US1),filed Aug. 20, 2010, entitled “RESIN COMPOSITION ELIMINATING VOLATILELOSS OF INITIATING SPECIES FOR THE PREPARATION OF PRINTED CIRCUIT BOARDLAMINATES”, which is hereby incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates in general to a composition of matter inwhich resins are polymerizable using non-volatile initiating species.More particularly, the present invention relates to compositions thatare especially adapted for resin formulations (e.g., polyphenylene ether(PPE) and modified PPE resin formulations) used in printed circuit boardlaminates. These compositions are made into prepreg dielectric sheets orcoated on a substrate and cured to form dielectric laminate structuresfor circuit packaging structures.

2. Background Art

One conventional technique for forming laminate circuit structures is toprovide a sheet of what is referred to as prepreg, which is a glasscloth impregnated with a resin solution which subsequently is eitherdried or at least partially cured.

Also, a similar type of resin is sometimes used without glass cloth andcoated onto metal, such as copper, for use as build up layers. These arecommonly referred to as resin coated copper (RCC) or polymer coatedcopper (PCC). Such prepregs are then laminated with copper foils formingcores. Cores are then processed further, such as forming vias andcircuitry thereon, and then laminated with additional prepregs andcopper foils to form composite laminate structures.

The resin used to prepare these printed circuit board laminatestypically includes a polymer, flame retardant, viscosity modifiers andan initiator. All of the components in the resin are non-volatile withthe exception of the free radical initiator. Volatile loss of theinitiator can occur during several of the steps in the preparation ofthe laminates (e.g., during resin preparation, during impregnation ofthe glass cloth, during coating of the copper, and/or during shipment,handling and curing of the prepreg). This volatile loss of the freeradical initiator can cause significant changes to the physicalproperties of the laminate. Specifically, volatile loss of the initiatorcan change the degree of cross-linking in the laminate, thus changingthe resultant mechanical properties. This can also lead toreproducibility problems as the laminate can outgas more or less of theinitiator, depending on the environment to which it is subjected.

Particularly useful resins for forming prepregs are described in U.S.Pat. No. 6,352,782 B2, often referred to as PPE, assigned to GeneralElectric Company, hereinafter sometimes referred to as the GE patent,and in U.S. Pat. No. 5,352,745, often referred to as modified PPE orAPPE, assigned to Asahi Kasei Kogyo Kabushiki Kaisha of Tokyo, Japan,hereinafter sometimes referred to as the Asahi patent. Both of thesepatents are incorporated herein by reference in their entirety.

The PPE resin as described in the GE patent is a reactively end cappedpoly(phenylene ether) compound cured with certain unsaturated compoundsfor synthesizing resins ideally adapted for impregnating fibrousreinforcement in the manufacture of circuit boards.

The modified PPE as described in the Asahi patent is a curablepolyphenylene ether resin composition comprising a reaction productobtained by reacting a polyphenylene ether with an unsaturatedcarboxylic acid or an acid anhydride and at least one cyanurate.Generally speaking, these compositions include about 98% to about 40% byweight of a curable polyphenylene ether resin comprising a reactionproduct obtained by reacting a polyphenylene ether with an unsaturatedcarboxylic acid or an acid anhydride, and 2% to 60% by weight, based onthe total weight of this and the previous components, of at least onecyanurate selected from the group consisting of triallyl isocyanurate(TAIL) and triallyl cyanurate. These compositions include an initiator.Generally speaking, the initiator is a peroxide of a low molecularweight compound, i.e., below about 700 grams per mole. These peroxidesare described in the Asahi patent at column 13, lines 10-23, and in theGE patent at column 12, lines 19-28.

An earlier PPE composition is described in U.S. Pat. No. 5,218,030,assigned to Asahi Kasei Kogyo Kabushiki Kaisha of Tokyo, Japan. Itdescribes the use of poly(phenylene ether) containing pendant allyl orpropargyl groups, triallylcyanurate or triallylisocyanurate, andoptionally an antimony-containing flame retardant. Other formulationsreplace this antimony flame retardant with bromine containing compounds.

Several problems have been encountered when using the PPE or modifiedPPE compositions incorporating low molecular weight initiators.(Hereinafter, the term PPE may be used for both PPE and modified PPE.)First, one problem is that the prepreg has component volatilitycharacterized by the volatilization of the low molecular weight peroxideinitiators. Second, following lamination, there is a marked out-gassingwhich has been attributed to the breakdown components of the lowmolecular weight initiator that do not enter into the reaction and aretrapped in the matrix and outgas upon lamination. Third, the inabilityto laminate the material after the prepreg has been exposed to wetprocessing. It is believed that this is due to the fact that the lowmolecular weight initiator is driven off when the prepreg is heated toremove any absorbed water. The first and third of these conditionsresult in poor crosslinking and, thus, degraded material and finalstructure properties. The second of these conditions results in thepropensity to delamination of the cured prepreg layers. The need tosolve these problems to improve the commercial viability of thecurrently available PPE and APPE products was recognized in U.S. Pat.No. 6,734,259 B1, assigned to International Business MachinesCorporation, hereinafter sometimes referred to as the IBM patent. TheIBM patent, which is described below, is incorporated herein byreference in its entirety.

The prepreg resin described in the IBM patent includes a polymerizationinitiator comprised of a peroxide functionalized polymer that isfragmented by heat to a plurality of free radical moieties, and arelatively inert moiety having a molecular weight greater than about1000. The high molecular weight polyperoxide material provided as aninitiator is described in the IBM patent at column 4, line 27—column 5,line 34. According to the IBM patent, the polyperoxide is preferably aperoxidized polystyrene. The IBM patent depicts a general structure of aperoxide functionalized polymer that can be used. A polymer in thegeneral structure depicted can be functionalized to incorporate peroxidegroups in pendant side chains or at the end groups. In other respects,the prepreg resin described in the IBM patent is like those described inthe GE patent and the Asahi patent. These compositions include about 98%to about 40% by weight of a curable polyphenylene ether resin, and 2% to60% by weight, based on the total weight of this and the previouscomponent, of triallyl isocyanurate. A bromated flame retardant is alsotypically included in these compositions.

Several problems have been encountered when using the PPE or modifiedPPE compositions incorporating the high molecular weight polyperoxidematerial described in the IBM patent as a polymerization initiator.First, one problem is that the physical properties of the prepreg (e.g.,glass transition temperature T_(g), mechanical properties, etc.) maychange because the free-radical initiators are bound to the polymer aspendant functional groups (rather than being bound in the backbone ofthe polymer). Second, upon heating to cure the prepreg, the free radicalinitiators bound to the polymer prior to heating are degraded togenerate only one initiating species (along with the relatively inertmoiety). A plurality of free radical moieties are generated only ifprior to heating the free-radical initiators are bound to the polymer asa plurality of pendant functional groups. Third, the generatedinitiating species is not bound to the polymer and, thus, is volatile.The generated initiating species (i.e., a number of t-butoxide moietieswhich will react with the TAIC to promote crosslinking) has a boilingpoint of 85° C., while the temperatures used to cure the prepregtypically exceed approximately 130° C. Because the generated initiatingspecies is volatile, its effectiveness as an initiator is significantlyreduced and the physical properties of the resulting material may changeuncontrollably from batch to batch.

These problems are also encountered when the polymerization initiatordescribed in the IBM patent is incorporated in other resin compositions(i.e., resin compositions other than PPE and modified PPE compositions).The PCB industry has recently migrated away from the traditional FR4epoxy based resins (due to lead-free requirements and the highersoldering temperatures associated with tin-silver-copper alloys). Hence,current resin coatings are typically no longer comprised of FR4 epoxies,rather they are more likely to be bismaleimide triazine (BT) resins orpolyphenylene oxide/triallyl-isocyanurate (PPO/TAIC) interpenetratingnetworks. Incorporating the high molecular weight polyperoxide materialdescribed in the IBM patent as a polymerization initiator into suchother resin compositions introduces the same problems noted above.

Therefore, a need exists for these problems to be solved to improve thecommercial viability of the currently available PPE and APPE products,as well as enhance the performance of other resin compositions that areused in printed circuit board laminates.

SUMMARY OF THE INVENTION

According to the preferred embodiments of the present invention, anenhanced prepreg for printed circuit board (PCB) laminates includes asubstrate and a resin applied to the substrate. The resin includes acurable polymer and a polymerization initiator polymer having a backbonewith a free radical initiator forming segment that breaks apart uponbeing subjected to heat to generate a plurality of non-volatileinitiating species. This resin composition eliminates possible volatileloss of the free radical initiator during all processing steps in thepreparation of PCB laminates. The resin may additionally include across-linking agent, flame retardant and viscosity modifiers. In oneembodiment, a sheet of woven glass fibers is impregnated with the resinand subsequently dried or cured. The glass cloth substrate may include asilane coupling agent to couple the resin to the substrate. In anotherembodiment, resin coated copper (RCC) is prepared by applying the resinto copper and subsequently curing the resin.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred exemplary embodiments of the present invention willhereinafter be described in conjunction with the appended drawings,where like designations denote like elements.

FIG. 1 is a block diagram illustrating a portion of a printed circuitboard (PCB) laminate in which a resin in accordance with the preferredembodiments of the present invention is applied to a glass fibersubstrate coated with a silane coupling agent.

FIG. 2 is a block diagram illustrating a portion of a printed circuitboard (PCB) laminate in which resin coated copper (RCC) is prepared byapplying to copper a resin in accordance with the preferred embodimentsof the present invention.

FIG. 3 is a flow diagram illustrating a method of making the printedcircuit board (PCB) laminate shown in FIG. 1 in accordance with thepreferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. Overview

In accordance with the preferred embodiments of the present invention,an enhanced prepreg for printed circuit board (PCB) laminates includes asubstrate and a resin applied to the substrate. The resin includes acurable polymer and a polymerization initiator polymer having a backbonewith a free radical initiator forming segment that breaks apart uponbeing subjected to heat to generate a plurality of non-volatileinitiating species. This resin composition eliminates possible volatileloss of the free radical initiator during all processing steps in thepreparation of PCB laminates. The resin may additionally include across-linking agent, flame retardant and viscosity modifiers. In oneembodiment, a sheet of woven glass fibers is impregnated with the resinand subsequently dried or cured. The glass cloth substrate may include asilane coupling agent to couple the resin to the substrate. In anotherembodiment, resin coated copper (RCC) is prepared by applying the resinto copper and subsequently curing the resin.

2. Detailed Description

A goal of the present invention is to provide a resin formulation thateliminates the volatile loss of the initiator during all steps in thepreparation of the laminates. Another goal of the present invention isto provide a resin formulation that will allow for simpler and moreefficient processing and handling of laminates and improve thereproducibility of their preparation.

In accordance with the preferred embodiments of the present invention, apolymer having a backbone with a free radical initiator forming segmentthat breaks apart upon being subjected to heat to generate a pluralityof non-volatile initiating species is provided as a polymerizationinitiator in a curable resin composition. In addition to this polymer,the curable resin composition may, for example, include a curablepolymer such as a curable polyphenylene ether (PPE) and at least onecyanurate selected from the group consisting of triallyl isocyanurateand triallyl cyanurate as a cross-linking agent. One skilled in the artwill appreciate that the curable resin composition may alternativelyinclude other conventional curable polymers and/or cross-linking agentssuch as those used in polyphenylene oxide/triallyl-isocyanurate(PPO/TAIC) interpenetrating networks. The polymerization initiatorpolymer in the curable resin composition preferably has a molecularweight in excess of 2000 and more preferably in excess of 3000.Likewise, each of the non-volatile initiating species generated by thispolymer when it breaks apart upon being subjected to heat preferably hasa molecular weight in excess of 1000 and more preferably in excess of3000. Three exemplary polymers that are particularly useful for use asthe polymerization initiator in the curable resin composition arerepresented below as “Polymer A”, “Polymer B”, and “Polymer C”, alongwith the decomposition products thereof.

wherein the non-volatile initiating species generated by Polymer A are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.

wherein the non-volatile initiating species generated by Polymer B are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.

wherein the non-volatile initiating species generated by Polymer C are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group. One skilled in the art will appreciatethat many other high molecular weight polymers having a backbone with afree radical initiator forming segment that breaks apart upon beingsubjected to heat to generate a plurality of non-volatile initiatingspecies are possible. In general, to be suitable as the polymerizationinitiator such other polymers preferably would also be thermally stableand relatively hydrophobic in nature, as well as exhibit reasonably lowdielectric properties.

Each of the above three exemplary polymers (i.e., Polymer A, Polymer Band Polymer C) preferably has a molecular weight in excess of 2000 andmore preferably in excess of 3000. Conventional processing conditionsinclude evaporating the solvent at between about 50° C. and 120° C., andthen curing at about 200° C. for about two hours, at about 200 PSI toabout 1000 PSI. One skilled in the art will appreciate that these arejust some of the conditions that can be used to cure the resin. Manyother conditions are possible.

Under heat, each of the above three exemplary polymers (i.e., Polymer A,Polymer B and Polymer C) breaks apart to generate the non-volatileinitiating species shown above. Each of these non-volatile speciespreferably has a molecular weight in excess of 1000 and more preferablyin excess of 3000. These non-volatile species will react with the TAICto promote cross-linking. Moreover, these non-volatile species alsoshould not interfere with the electrical or mechanical properties of thecured resin, i.e., the properties of the cured resin should not differsignificantly from those described in the Asahi and GE patents. Thus,each of the above three exemplary polymers will not be subject to anysignificant evaporation from the PPE composition, nor will it evaporateto any significant extent if the composition is exposed to water and thewater is subsequently dried; moreover, under heat, each of thenon-volatile initiating species will not volatilize because of its highmolecular weight. Thus, by using a high molecular weight polymer havinga backbone with a free radical initiator forming segment that breaksapart upon being subjected to heat to generate a plurality ofnon-volatile initiating species, the three major problems encounteredwith the PPE resin system in the Asahi and GE patents have beenovercome.

In addition, by using a high molecular weight polymer having a backbonewith a free radical initiator forming segment that breaks apart uponbeing subjected to heat to generate a plurality of non-volatileinitiating species, the three major problems encountered with the PPEresin system in the IBM patent (which uses a high molecular weightpolyperoxide initiator functionalized to incorporate peroxide groups inpendant side chains or at the end groups) are overcome. First, thephysical properties of the prepreg (e.g., glass transition temperatureT_(g), mechanical properties, etc.) do not change because thefree-radical initiators are bound in the backbone of the polymer (ratherthan being bound as pendent functional groups). Second, a plurality ofnon-volatile initiating species are generated when the free radicalinitiator forming segment of the polymer backbone breaks apart uponbeing subjected to heat. This reduces the concentration of initiatingspecies required to cure the prepreg. Third, each of the non-volatileinitiating species generated will not volatilize because of its highmolecular weight. With both initiating species not being volatile, thephysical properties of the laminate are highly reproducible from batchto batch.

To summarize, although the polymerization initiator described in the IBMpatent does provide a non-volatile prepreg during shipment, thatinitiator has several drawbacks. The most significant drawback is thatonce the free radical species is generated, it becomes volatile. Thisleads to highly un-reproducible material properties. Additionally,higher concentration of initiating species is required. The physicalproperties of the resulting polymer change as well.

The resin composition in accordance with the preferred embodiments ofthe present invention has several advantages over the polymerizationinitiator described in the IBM patent: the resin composition inaccordance with the preferred embodiments of the present inventionreduces the required initiator concentration; the physical properties ofthe resulting polymer do not change; and, most importantly, at no pointin the entire process does the resin composition contain any volatilecomponents. This leads to a highly reproducible process. Thisreproducibility, in turn, allows for simplification of and improvedefficiency in processing and handling during preparation of thelaminates. Also, the resin composition allows for safer processing andhandling because the initiating species is no longer a volatile organiccompound.

A polymer with a free radical initiator forming segment built into itsbackbone in accordance with the present invention (also referred toherein as a “polymerization initiator polymer”) can be solely used inthe preparation of laminate or can be incorporated as a blend with otherconventional polymers used in laminate production. For example, apolymerization initiator polymer in accordance with the presentinvention (e.g., Polymer A) can be used alone in the preparation oflaminate or, alternatively, that same polymerization initiator polymercan be blended with other conventional polymers used in laminateproduction (e.g., polyphenylene oxide/triallyl-isocyanurate (PPO/TAIC)interpenetrating networks).

Ideally, it is preferable to use the minimum amount of thepolymerization initiator polymer required to ensure complete andefficient curing of the laminate. Typically, the concentration of theconventional initiator used in laminate preparation is less than 1 wt %.The polymerization initiator polymer in accordance with the preferredembodiment of the present invention is typically blended with PPO orother conventional polymers used in laminate production at comparable(or lower) levels of concentration. In this fashion, any change to thebase resin will be minimized because the polymerization initiatorpolymer is present in the formulation at comparably low levels.Typically, the polymerization initiator polymer will have the exactphysical properties of the base resin (e.g., Polymer A has the exactphysical properties of PPO, as does Polymer B and Polymer C). Once thepolymerization initiator polymer and the base resin are combined withthe viscosity modifiers and flame retardant, the resulting resincomposition may be pressed into a glass cloth, for example. Upon heatingthe prepreg, the polymerization initiator polymer degrades to form twonon-volatile radical initiating species, thus curing the polymer. Usingthe polymerization initiator polymer eliminates possible volatile lossof the free radical initiator during all processing steps in thepreparation of laminates.

An example of an approach for synthesizing Polymer A is representedbelow as “Exemplary Synthesis of Polymer A”. In general, apolymerization initiator polymer in accordance with the presentinvention can be synthesized in any number of ways or may be obtained asa commercially available polymer. The present invention relates to theuse of such a polymer (i.e., a polymer having a free radical initiatorforming segment built into its backbone that breaks apart upon beingsubjected to heat to generate two non-volatile initiating species) as apolymerization initiator regardless of the synthetic approach used forits preparation.

Exemplary Synthesis of Polymer A

wherein X is a hydrogen atom or methyl group.

wherein X is a hydrogen atom or methyl group.

wherein X is a hydrogen atom or methyl group.

wherein X is a hydrogen atom or methyl group, and x is a hydrogen atomor methyl group.

wherein X is a hydrogen atom or methyl group, and x is a hydrogen atomor methyl group.

wherein X is a hydrogen atom or methyl group, and x is a hydrogen atomor methyl group.

In an exemplary embodiment of the present invention, there is (a) 98% to40% by weight based on the total weight of components (a) and (b) of acurable polyphenylene ether (PPE) resin, preferably comprising areaction product obtained by reacting a polyphenylene ether with anunsaturated carboxylic acid or an acid anhydride; and (b) 2% to 60% byweight based on the total weight of components (a) and (b) of at leastone cyanurate selected from the group consisting of triallylisocyanurate and triallyl cyanurate. Other components may optionally beadded as described in the Asahi and GE patents, such as an epoxy resinand a curing agent, to which the polymerization initiator polymer inaccordance with the present invention is added. Preferably thepolymerization initiator polymer is added from about 0.1 to about 10parts by weight and, more preferably, from 0.1 to 8 parts by weightbased on 100 parts by weight of the components (a) and (b). Thesecompositions may also contain filler materials, such as silica. Thepolymerization initiator polymer is a high molecular weight (preferablyin excess of 2000 and, more preferably, in excess of 3000) polymerhaving a backbone with a free radical initiator forming segment thatbreaks apart upon being subjected to heat to generate a plurality ofnon-volatile initiating species (each having a molecular weightpreferably in excess of 1000 and, more preferably, in excess of 3000).The polymerization initiator polymer may be, for example, one or more ofthe above three exemplary polymers (i.e., Polymer A, Polymer B and/orPolymer C).

The particular resin and initiators described herein can be eithermanufactured into prepreg (shown in FIG. 1, described below) or resincoated copper (shown in FIG. 2, described below) with improved storageand handling behavior. These materials are then processed in aconventional manner resulting in low dielectric, highly stable,hydrophobic laminated electronic packaging structures (e.g., printedcircuit boards and laminate chip carriers) that do not suffer fromout-gassing during the curing and later heating stages. Significantly,each of the non-volatile initiating species generated when the freeradical initiator forming segment of the polymer backbone breaks apartupon being subjected to heat will not volatilize because of its highmolecular weight.

FIG. 1 is a block diagram illustrating a portion of a printed circuitboard (PCB) laminate 100 in which a resin 130 in accordance with thepreferred embodiments of the present invention is applied to a glassfiber substrate 110 having its surface modified by a silane couplingagent 120.

Typically, a silane coupling agent is applied to the surface of a glassfiber substrate. In addition, an optional silane composition may beapplied to the surface of the glass fiber substrate (to which the silanecoupling agent was earlier applied) to form a hydrophobic silanecoating, which is an intermixed layer containing both silanes. Such ahydrophobic silane coating for preventing conductive anode filament(CAF) is disclosed in U.S. patent application Ser. No. 12/718,213,assigned to International Business Machines Corporation, which is herebyincorporated herein by reference in its entirety.

The resin 130 may be any conventional base resin that is modified inaccordance with the preferred embodiments of the present invention toinclude a polymerization initiator polymer having a backbone with a freeradical initiator forming segment that breaks apart upon being subjectedto heat to generate a plurality of non-volatile initiating species. Forexample, the resin 130 may a polyphenylene ether (PPE) resin, a modifiedPPE (APPE) resin, an FR4 epoxy resin, a bismaleimide triazine (BT)resin, or a polyphenylene oxide/triallyl-isocyanurate (PPO/TAIC)interpenetrating network, each modified to include one or more of theabove three exemplary polymers (i.e., Polymer A, Polymer B and/orPolymer C) as the polymerization initiator.

The substrate 110 is conventional and may be any suitable substrate. Forexample, the substrate 110 may be woven glass cloth.

The silane coupling agent 120 is conventional and may be any suitablesilane coupling agent. The silane coupling agent typically consists ofan organofunctional group to bind to the resin coating 130 and ahydrolyzable group that binds to the surface of the substrate 110. Forexample, the silane coupling agent may bevinylbenzylaminoethylaminopropyltrimethoxysilane ordiallylpropylisocyanurate-trimethoxysilane. Typically, the silanecoupling agent is a monolayer thick.

The optional silane composition used to form the hydrophobic silanecoating (an intermixed layer containing both silanes) typically includesa silane having a general formula structure R₁—Si—R₍₂₋₄₎, wherein R₁ isa functional group that is reactive with alcohols, water and/or surfacesilanols, and wherein R₂, R₃ and R₄ are each a functional group that ishydrophobic and non-reactive (i.e., R₂, R₃ and R₄ are each non-reactivewith the alcohols, water and/or surface silanols with which R₁ isreactive). Examples of suitable silanes for the silane compositioninclude (without limitation) chlorotrimethylsilane (i.e., (CH₃)₃SiCl,also known as trimethylsilylchloride or TMSCl), hexamethyldisilazane(i.e., [(CH₃)₃)Si]₂NH, also known as HMDS or HMDZ),perfluorooctyl-1H,1H,2H,2H-dimethylchlorosilane (i.e., C₁₀H₁₀CF₁₃Si),and (3,3,3-trifluoropropyl)dimethyl-chlorosilane (i.e., C₅H₁₀CF₃Si); andcombinations thereof.

FIG. 2 is a block diagram illustrating a portion of a printed circuitboard (PCB) laminate 200 in which resin coated copper (RCC) is preparedby applying to copper 220 a resin 230 in accordance with the preferredembodiments of the present invention.

The resin 230 may be any conventional resin that is modified inaccordance with the preferred embodiments of the present invention toinclude a polymerization initiator polymer having a backbone with a freeradical initiator forming segment that breaks apart upon being subjectedto heat to generate a plurality of non-volatile initiating species. Forexample, the resin 130 may a polyphenylene ether (PPE) resin, a modifiedPPE (APPE) resin, an FR4 epoxy resin, a bismaleimide triazine (BT)resin, or a polyphenylene oxide/triallyl-isocyanurate (PPO/TAIC)interpenetrating network, each modified to include one or more of theabove three exemplary polymers (i.e., Polymer A, Polymer B and/orPolymer C) as the polymerization initiator.

The substrate 210 is conventional and may be any suitable substrate. Forexample, the substrate 210 may be an organic or inorganic substratehaving a layer of copper 220 provided on the surface thereof.

The layer of copper 220 is conventional and may be any suitable copperfilm, coating, foil or the like. The layer of copper 220 may be, forexample, a copper coating deposited onto the surface of the substrate210 utilizing any suitable conventional process. Alternatively, anysuitable metal may be used in lieu of the layer of copper 220.

FIG. 3 is a flow diagram illustrating a method 300 of making the printedcircuit board (PCB) laminate 100 (shown in FIG. 1) in accordance withthe preferred embodiments of the present invention. In the method 300,the steps discussed below (steps 310-340) are performed. These steps areset forth in their preferred order. It must be understood, however, thatthe various steps may occur at different times relative to one anotherthan shown, or may occur simultaneously. Moreover, those skilled in theart will appreciate that one or more of the steps may be omitted.

Method 300 begins when a substrate that includes glass fiber is cleaned(step 310). The substrate is conventional and may be any suitablesubstrate that includes glass fiber. For example, the substrate may bewoven glass cloth. The substrate is cleaned utilizing any suitableconventional cleaning process, such as the industry standard process forcleaning woven glass fabric described below.

Glass fiber is typically received at the glass weaver on a bobbin andcontains a sizing agent typically present at approximately 1.5 wt % ofthe glass filament. The sizing agent is a starch and oil-basedformulation that serves as an anti-static and slip agent which impartsstrength to the fabric during the weaving process. The glass filament tobe woven in the machine direction may contain 1 wt % PVA to impartadditional mechanical strength during the warping process. Followingweaving, the fabric is cleaned via an industry standard process:

1) The fabric is wound on a mandrel and subjected to temperatures inexcess of 500 C for several hours (a process known to those skilled inthe art as “carmelizing” as the fabric takes on a golden brown color).

2) Mandrels are subsequently subjected to temperatures greater than 200C for several days (in order to permit the temperature in the center ofthe core to equilibrate with the temperature of the fabric surface).

3) The fabric is permitted to cool to ambient temperature overnight.

The method 300 continues with modification of the surface of thesubstrate with a silane coupling agent (step 320). The silane couplingagent is conventional and may be any suitable silane coupling agent. Forexample, the silane coupling agent may bevinylbenzylaminoethylaminopropyltrimethoxysilane ordiallylpropylisocyanurate-trimethoxysilane. The silane coupling agent isapplied to the surface of the substrate using any suitable conventionalsurface modification process.

Steps 310 and 320 may be omitted in favor of obtaining a conventionalglass fiber substrate having its surface already modified with a silanecoupling agent. Such surface modified glass fiber substrates arecommercially available from glass weavers. The surface modificationprocesses utilized by these glass weavers may include elements that areconsidered proprietary to the glass weaver.

Typical process parameters of conventional surface modificationprocesses include the addition of a surfactant to a silane bath (i.e.,typically, the glass fabric is dipped in a silane bath) to enhancewetting of the glass fabric as well as prevent foaming. The silanecoupling agent concentration in the silane bath may be as high as 1 wt%, for example, though it is typically much less. The silane bath istypically acidic (pH 3-5) to prevent self-condensation of the silane.

In one exemplary conventional surface modification process, the glassfabric may be dipped into 0.1%-0.5% silane coupling agent/water solution(or water-ethanol solution), and then air-dried. The glass fabric maythen be placed in a desiccator at 110-120° C. for 5-10 minutes to curethe silane coupling agent on the surface of the substrate.

In another conventional surface modification process, an alcoholsolution is used for silylating the surface of the substrate with asilane coupling agent. A 2% silane solution can be prepared in asuitable alcohol (e.g., methanol, ethanol, isopropanol, and the like).The surface of the substrate can be wiped, dipped, or sprayed with thissolution. If the substrate is dipped into the solution, a sufficientsubmersion time (e.g., one or two minutes) may be necessary to allowsilane migration to the surface of the substrate. The substrate is thendried (e.g., air-dried). After the surface of the substrate dries,excess material can be gently wiped, or briefly rinsed off with alcohol.The layer of silane coupling agent may then be cured on the surface ofthe substrate for 5-10 minutes at 110 C, or for 24 hours at ambienttemperature.

The method 300 may continue with the drying of the surface of thesubstrate (i.e., the treated glass fabric) dried using any suitableconventional methodology known to those skilled in the art (step 330).For example, the treated glass fabric may be dried at 110-120° C. for5-10 minutes. However, step 330 may be at least partially performed aspart of step 320, discussed above, when the silane coupling agent iscured on the surface of the substrate.

The coated substrate (i.e., silane coupling coating/substrate) may thenbe further processed using a conventional resin modified with apolymerization initiator polymer in accordance with the preferredembodiments of the present invention and conventional PCB fabricationtechniques (step 340). For example, a conventional resin (e.g.,polyphenylene ether (PPE) resins, a modified PPE (APPE) resins, FR4epoxy resins, bismaleimide triazine (BT) resins, polyphenyleneoxide/triallyl-isocyanurate (PPO/TAIC) interpenetrating networks, andthe like) may be modified to include a polymerization initiator polymerhaving a backbone with a free radical initiator forming segment thatbreaks apart upon being subjected to heat to generate a plurality ofnon-volatile initiating species. This modified resin may be applied tothe coated substrate using any suitable conventional methodology knownto those skilled in the art. After which the laminate is subjected tocuring conditions, e.g., heated under vacuum, as known in the art, whichresults in a crosslinked phase that is covalently bound to the glassfibers to define a laminate, or laminated PCB.

One skilled in the art will appreciate that many variations are possiblewithin the scope of the present invention. Thus, while the presentinvention has been particularly shown and described with reference topreferred embodiments thereof, it will be understood by those skilled inthe art that these and other changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A resin, comprising: a curable polymer; and apolymerization initiator polymer having a backbone with a free radicalinitiator forming segment that breaks apart upon being subjected to heatto generate a plurality of non-volatile initiating species.
 2. The resinas recited in claim 1, wherein the polymerization initiator polymer is amodified polyphenylene ether (PPE) that is blended in the resin with aconventional resin that includes an unmodified PPE.
 3. The resin asrecited in claim 1, wherein the polymerization initiator polymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 4. The resin as recited in claim 1,wherein the polymerization initiator polymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 5. The resin as recited in claim 1,wherein the polymerization initiator polymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 6. A cured resin comprising the reactionproduct of a resin comprising: a curable polymer; and a polymerizationinitiator polymer having a backbone with a free radical initiatorforming segment that breaks apart upon being subjected to heat togenerate a plurality of non-volatile initiating species.
 7. The curedresin as recited in claim 6, wherein the polymerization initiatorpolymer is a modified polyphenylene ether (PPE) that is blended in theresin with a conventional resin that includes an unmodified PPE.
 8. Thecured resin as recited in claim 6, wherein the polymerization initiatorpolymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 9. The cured resin as recited in claim 6,wherein the polymerization initiator polymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 10. The cured resin as recited in claim6, wherein the polymerization initiator polymer is

and wherein the non-volatile initiating species generated are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 11. A resin, comprising: a curablepolymer; a polymerization initiator polymer having a backbone with afree radical initiator forming segment that breaks apart upon beingsubjected to heat to generate a plurality of non-volatile initiatingspecies, wherein the polymerization initiator polymer is selected fromthe group consisting of Polymer A, Polymer B, Polymer C, andcombinations thereof; wherein Polymer A is

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group; wherein Polymer B is

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group; and wherein Polymer C is

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 12. The resin as recited in claim 11,wherein the polymerization initiator polymer is Polymer A and whereinthe non-volatile initiating species generated by Polymer A are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 13. The resin as recited in claim 11,wherein the polymerization initiator polymer is Polymer B and whereinthe non-volatile initiating species generated by Polymer B are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 14. The resin as recited in claim 11,wherein the polymerization initiator polymer is Polymer C and whereinthe non-volatile initiating species generated by Polymer C are

wherein X is a hydrogen atom or methyl group, and wherein x is ahydrogen atom or methyl group.
 15. The resin as recited in claim 11,wherein each of the plurality of non-volatile initiating species has amolecular weight in excess of
 1000. 16. The resin as recited in claim11, wherein each of the plurality of non-volatile initiating species hasa molecular weight in excess of
 3000. 17. The resin as recited in claim11, wherein the curable polymer is a base resin selected from a groupconsisting of a polyphenylene ether (PPE) resin, a modified PPE (APPE)resin, an FR4 epoxy resin, a bismaleimide triazine (BT) resin, apolyphenylene oxide/triallyl-isocyanurate (PPO/TAIC) interpenetratingnetwork, and combinations thereof.
 18. The resin as recited in claim 11,wherein the curable polymer includes polyphenylene oxide (PPO).